CBSE CLASS X SCIENCE

  CBSE Class 10 Chemistry Chapter 1 - Chemical Reactions and Equations Exercise 4 What is a balanced chemical equation? Why should chemical equations be balanced?  What is a balanced chemical equation? A balanced chemical equation is a representation of a chemical reaction where the number of atoms of each element is equal on both sides of the equation (reactants and products). This means that the total mass of reactants equals the total mass of products. For example: Unbalanced: H2 + O2 → H2O Balanced: 2H2 + O2 → 2H2O In the balanced equation, we have 4 hydrogen atoms and 2 oxygen atoms on both sides. Why should chemical equations be balanced? Chemical equations must be balanced for several important reasons: 1. Law of Conservation of Mass This fundamental law states that matter cannot be created or destroyed in a chemical reaction. The total mass of reactants must equal the total mass of products. Balancing ensures this law is satisfied by having equal numbers of ...

  CBSE Class 10 Chemistry Chapter 1 - Chemical Reactions and Equations Exercise 3 What happens when dilute hydrochloric acid is added to iron fillings?  (a) Hydrogen gas and iron chloride are produced.  (b) Chlorine gas and iron hydroxide are produced.  (c) No reaction takes place.  (d) Iron salt and water are produced. Iron is a moderately reactive metal that can displace hydrogen from dilute acids. The reaction that occurs is: Fe(s) + 2HCl(aq) → FeCl2(aq) + H2(g) Breaking this down: Iron fillings react with hydrochloric acid Iron displaces hydrogen from the acid This produces iron(II) chloride (FeCl2) and hydrogen gas You would observe bubbling as hydrogen gas is released Let me check each option: (a) Hydrogen gas and iron chloride are produced - CORRECT This matches exactly what happens: H2(g) is evolved and FeCl2 (iron chloride) is formed. (b) Chlorine gas and iron hydroxide are produced - INCORRECT Chlorine gas is not produced in this reaction, ...

CBSE Class 10 Chemistry Chapter 1 - Chemical Reactions and Equations Exercise 2 Fe2O3 + 2Al → Al2O3 + 2Fe The above reaction is an example of a (a) combination reaction. (b) double displacement reaction. (c) decomposition reaction. (d) displacement reaction. Looking at the reaction: Fe2O3 + 2Al → Al2O3 + 2Fe Aluminum (Al) displaces iron (Fe) from iron oxide (Fe2O3) Iron is pushed out of its compound and forms free iron metal Aluminum takes iron's place and forms aluminum oxide (Al2O3) This follows the general pattern: A + BC → AC + B Where: A = Al (more reactive metal) BC = Fe2O3 (compound containing less reactive metal) AC = Al2O3 (new compound formed) B = Fe (displaced metal) Let me check each option: (a) Combination reaction - This would be A + B → AB (two substances combining to form one). This doesn't fit since we have two products. (b) Double displacement reaction - This would be AB + CD → AD + CB (two compounds exchanging ions). This doesn't fit since we s...

CBSE Class 10 Chemistry Chapter 1 - Chemical Reactions and Equations Exercise 1 Which of the statements about the reaction below are incorrect?  2PbO(s) + C(s) → 2Pb(s) + CO2 (g)  (a) Lead is getting reduced.  (b) Carbon dioxide is getting oxidised.  (c) Carbon is getting oxidised.  (d) Lead oxide is getting reduced. Looking at the reaction: 2PbO(s) + C(s) → 2Pb(s) + CO2(g) Initial oxidation states: In PbO: Pb = +2, O = -2 In C: C = 0 Final oxidation states: In Pb: Pb = 0 In CO2: C = +4, O = -2 Changes: Lead: +2 → 0 (decrease in oxidation state = reduction) Carbon: 0 → +4 (increase in oxidation state = oxidation) Now examining each statement: (a) Lead is getting reduced - CORRECT Lead's oxidation state decreases from +2 to 0. (b) Carbon dioxide is getting oxidised - INCORRECT CO2 is a product, not a reactant. It's not "getting" oxidized - it's the result of carbon's oxidation. The carbon within CO2 is already in the +4 oxidation state. (c) Carbon...